1. Field of the Invention
The present invention relates to switches to be used for turning on or off brake lights in response to stepping on the brake pedal of a vehicle.
2. Background Art
A push-type vehicle switch has been widely used for controlling brake lights in response to stepping on the brake pedal of a vehicle, to be more specific, the push switch turns on the brake lights when a driver steps on the brake pedal, and turns off the brake lights when the driver releases the pedal. Such a conventional vehicle switch is described hereinafter with reference to FIGS. 15 and 16.
FIG. 16 shows a sectional view of a conventional vehicle switch. This vehicle switch has housing 1 made of insulating resin, shaped like a box, and open upward; and operating unit 2 accommodated in housing 1 and movable vertically. Operating shaft 2A of operating unit 2 slides along cylinder 7A of cover 7 covering the opening at the top of housing 1. A plurality of fixed contacts 3 is provided to housing 1 and terminals 3A drawn from fixed contacts 3 protrude from the outer bottom of housing 1. Movable contacts 4 made of metal are urged by push-up spring 5 that is somewhat compressed and placed between the bottom of housing 1 and contacts 4, so that movable contacts 4 are brought into contact with fixed contacts 3 at the bottom of each one of fixed contacts 3. Fixed contacts 3 are thus coupled to each other electrically via movable contacts 4. Return spring 6 is somewhat compressed and placed between the lower face of operating unit 2 and the inner bottom of housing 1 for urging operating unit 2 upward. Operating shaft 2A, i.e. upper end of operating unit 2, protrudes upward from cylinder 7A provided at the center of cover 7. Conventional vehicle switch 10 is constructed as discussed above.
Vehicle switch 10 thus constructed is mounted to brake-pedal 11 on a side as laterally shown in FIG. 15, while operating shaft 2A of operating unit 2 is pressed by arm 11A. Terminals 3A of fixed contacts 3 protruding from the outer bottom of housing 1 are coupled to brake lights (not shown) and an electronic circuit via connector 12.
When brake pedal 11 is not stepped on, operating shaft 2A is pressed downward. This state is called “a steady state”, hereinafter. In the steady state, operating shaft 2A compresses push-up spring 5 and return spring 6, so that movable contacts 4 move downward and leave fixed contacts 3. Thus, movable contacts 4 are not contact with each other electrically, and the brake lights are turned off.
The state in which brake pedal 11 is stepped on is illustrated with alternate long and two short dashes lines in FIG. 15. This state is called “an operated state”, hereinafter. In the operated state, arm 11A leaves shaft 2A and the pressing force is removed, so that operating unit 2 moves upward due to resilient restoring force of return spring 6, and at the same time, movable contacts 4 are elastically urged against fixed contacts 3 by push-up spring 5 as shown in FIG. 16, so that fixed contacts 3 are electrically connected with each other for turning on the brake lights.
Vehicle switch 10 is generally used near brake pedal 11 of the vehicle, i.e. at a place having a lot of dampness, dust, gas or the like. Lubricating agent is generally applied to arm 11A pressing operating shaft 2A, so that the agent, gas, dust and dampness can enter into vehicle switch 10 and attach to fixed contacts 3 or movable contacts 4. As a result, carbide or silicon compound is formed on the surface of contacts 3 and 4, thereby inviting failure in electrical on/off of the contacts.
To prevent this failure, the switch is devised to be structured air-tightly in general. For example, operating shaft 2A and cylinder 7A are covered with a rubber cap, or space between housing 1 and cover 7 is sealed with adhesive or shielding member. This structure; however, requires a greater number of components and a longer time for assembly.
Prior art documents pertinent to the present invention are, e.g. Unexamined Japanese Patent Publication Nos. 2004-342437, and 2006-92777.